What is Argo?

Argo is a global array of 3,800 free-drifting profiling floats that measures thetemperature
and salinity of the upper 2000 m of the ocean. This allows, for the first time,
continuous monitoring of the temperature, salinity, and velocity of the upper ocean, with
all data being relayed and made publicly available within hours after collection.

Positions of the floats that have delivered data within the last 30
days
:

Maps displaying statistics about the Argo array, including its extensions into high latitudes and marginal seas,
bio-geochemical sensors, communication systems, float type, etc.,
can be found in the
map section on the Argo Information Centre website.

Why do we need Argo?

We are increasingly concerned about global change and its regional impacts. Sea level is
rising at an accelerating rate of 3 mm/year, Arctic sea ice cover is shrinking and high
latitude areas are warming rapidly. Extreme weather events cause loss of life and enormous
burdens on the insurance industry. Globally, 8 of the 10 warmest years since 1860, when
instrumental records began, were in the past decade.

These effects are caused by a mixture of long-term climate change and natural variability.
Their impacts are in some cases beneficial (lengthened growing seasons, opening of Arctic
shipping routes) and in others adverse (increased coastal flooding, severe droughts, more
extreme and frequent heat waves and weather events such as severe tropical cyclones).

Understanding (and eventually predicting) changes in both the atmosphere and ocean are needed
to guide international actions, to optimize governments' policies and to shape industrial
strategies. To make those predictions we need improved models of climate and of the entire
earth system (including socio-economic factors).

Lack of sustained observations of the atmosphere, oceans and land have hindered the
development and validation of climate models. An example comes from a recent analysis
which concluded that the currents transporting heat northwards in the Atlantic and
influencing western European climate had weakened by 30% in the past decade. This result
had to be based on just five research measurements spread over 40
years. Was this change part of a trend that might lead to a major change in the Atlantic
circulation, or due to natural variability that will reverse in the future, or is it an
artifact of the limited observations?

In 1999, to combat this lack of data, an innovative step was taken by scientists to greatly
improve the collection of observations inside the ocean through increased sampling of old
and new quantities and increased coverage in terms of time and area.

That step was
Argo.

argo.avi
is a float animation that explains the purpose and method of Argo.

Where is Argo now?

Argo deployments began in 2000, and by November 2007, the millionth profile was collected.
Today, even with close to 4000 active floats, there are still some areas of the ocean
that are over-populated while others have gaps that need to be filled with additional floats.
Today's tally of floats is shown in the figure above and additional float statistics can be
found here. To maintain the Argo array,
national programs need to
provide about 800 floats per year.

The original global Argo array was designed for the open ocean excluding seasonal sea-ice zones and marginal seas.
Thanks to both two-way communication and ice-sensing algorithms on floats, these technical
limitations are largely mitigated. The concept of Argo has always been of a spatially complete global array.
Therefore, including seasonal sea-ice zones and marginal seas moves the target number of Argo
floats from 3000 to 3800.

In addition to the globalization of core Argo described above, there are several Argo enhancements
that are in various stages of development
and implementation.
These include extended coverage to the ocean bottom, additional floats equipped with bio-geochemical
sesnors, and enhanced spatial coverage in boundary current regions and
equatorial regions.

Besides float deployment, Argo has worked hard to develop two separate data streams:
real time and delayed mode. A real time data delivery and quality control system has
been established that delivers 90% of profiles to users via two global data centers (GDACs)
within 24 hours. A delayed mode quality control system (DMQC) has been established and
65% of all eligible profiles have had DMQC applied.

Float reliability has improved
almost every year and the float lifetime has been extended. Argo has developed a large user
community in universities, government labs and meteorological/climate analysis/forecasting
centers. The need for global Argo observations will continue indefinitely into the future,
though the technologies and design of the array will evolve as better instruments are built,
models are improved, and more is learned about ocean variability.

Who Collaborates with Argo?

Argo is a major contributor to the WCRP
's Climate Variability and Predictability Experiment
(CLIVAR) project and to the Global
Ocean Data Assimilation Experiment (GODAE). The Argo array is part of the Global Climate Observing
System/Global Ocean Observing System OceanView
GCOS
/GOOS).